Gravity was one of the unqualified successes of 2013, earning universal acclaim, awards season love, and approximately a gazillion dollars at the box office. But the road to the theater wasn’t exactly easy. One of the tricky aspects was the casting. In 2010, Gravity was practically a revolving door of movie stars.

Two that were attached to star for some time were Angelina Jolie and Robert Downey Jr. Eventually, both dropped out and were replaced by Sandra Bullock and George Clooney. In a new interview, director Alfonso Cuaron explains why, exactly, the original casting failed to work out. Hit the jump to read his comments.

The reasoning behind Jolie’s departure isn’t all that surprising. Basically, it came down to scheduling.

We started developing stuff [trying] to figure out the technology. And the luxury [was] that we could try many things. And part of that was conversations with actors. I had conversations with Angelina, but then she went to do one film, and then she was going to direct [Unbroken]. Something happens, you part ways.

The other film Cuaron mentions seems to be Maleficent, as Jolie was announced for the lead role around the same time that she was turning down Gravity.

The explanation for Downey’s exit is more interesting.

It became very clear that, as we started to nail the technology, or narrow the technology, that was going to be a big obstacle for his performance. I think Robert is fantastic if you give him the freedom to completely breathe and improvise and change stuff. [But] we tried one of these technologies and it was not compatible. And, after that, we [had a] week that we pretended as if nothing was happening and then we talked and said, ‘This is not going to work. This is tough.’

As much as we love Downey, Cuaron’s explanation makes perfect sense. In his replacement, Cuaron found someone who could could exude charm, add A-list cachet, and stick to a script. The choice of Bullock worked out very well, too, though we’re sure Jolie would’ve done a fine job as well.

Head to THR for the rest of Cuaron’s interview, and then tell us what you think. Would Gravity have been better with its original cast?